B. fragilis strains, especially in the US, are
virtually always susceptible to metronidazole, carbapenems, and beta-lactam
antibiotics. Although isolated cases of resistance to single agents have been
reported, multidrug-resistant (MDR) B.
fragilis strains are exceptionally rare. In May 2013, an MDR B. fragilis strain was isolated from the
bloodstream and intra-abdominal abscesses of a patient who had recently
received health care in India. The organism was resistant to metronidazole,
imipenem, piperacillin/tazobactam, clindamycin, tcefotetan, ampicillin/sulbactam,
and moxifloxacin. It was susceptible to minocycline, linezolid, and
tigecycline. He was successfully treated with linezolid and ertapenem. This is
only the second published case of MDR B.
fragilis in the US.
Although
B. fragilis has long been considered
reliably susceptible to a number of broad-spectrum anti-anaerobic drugs, this case and others like it suggest clinicians should no longer rely on cumulative
susceptibility data from surveys alone to direct treatment and should consider
requesting susceptibility testing when treating serious infections caused by B. fraglis. They also underscore the
need for improved antibiotic stewardship.
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